There is conventionally known a valve timing controller for shifting a relative rotational phase between two rotary elements, which rotate respectively in response to the crankshaft and the camshaft, by a differential gear system composed mainly of a planetary gear.
For example, DE-4110195C2 discloses a valve timing controller which includes a sprocket as one rotary element rotating in response to a crankshaft, and a gear part as the other rotary element rotating in response to the camshaft, having a differential gear system composed mainly of a planetary gear between the sprocket and the other rotary element. Further, a stopper is provided in the sprocket and the gear part for regulating a phase shift angle of a relative rotational phase of the gear part to the sprocket. A planetary motion due to engagement of an internal gear part located in an inner wall of the sprocket and an external gear part located in the planetary gear of the gear part is converted into a relative rotational motion of the gear part to the sprocket. In addition, the gear part moves freely in the thrust direction to the sprocket and is nearly in a free state.